Depth-profiling with PIXEPIXE opens with the opportunity for depth profiling an additional dimension in art and artifact analysis. Sequences of layers can be analyzed to probe the preparation procedure and the preparation techniques.

Range of protons in matter

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 1 2 3 4 5

proton energy [MeV]

rang

e [

mm

]

carbonirongold

Simple Approximation Formula for Range Calculations

R cmA

R cm

[g/cm ]A

AA

Aair

A

A

[ ] . [ ]≈ ⋅ ⋅ ⋅

≡≡

−32 10 4

3

ρ

ρ density in atomic number of absorber

Example: range R208 of 3 MeV protons in Lead (A=208, ρ=11.35 g/cm3)

R

R

208

208

≈ ⋅ ⋅ ⋅

≈ ⋅ =

−

−

32 10208

113513

529 10 53

4

3

..

[ ]

.

cm

cm mµ

0

2

4

6

8

10

12

14

0 20 40 60 80 100 120 140 160 180

proton range in air Rair [cm]

prot

on e

nerg

y [M

eV]

3 MeV protons on Nickel/Iron layer

Confirm the observed range of the 3 MeV proton beam in Nickel!A=58, ρ=8.9 g/cm3

R

Robserved is about

58

58

≈ ⋅ ⋅ ⋅

≈ ⋅ =

−

−

32 1058

8 913

35 10 3532

4

3

..

[ ]

.

cm

cm mmµ

µ

Beam Stopping in Reality

7 MeV beam energyR≈60 cm

0.3 MeV beam energyR≈1cm

PIXE: experimental set-upprotons from accelerator

• beam exit: thin Kapton foil• moveable mirror inflects

laser on beam axis• two detectors at 135°• shielding against radiation

from exit foil• xy table• camcorder surveys and

documents beam spot

HPGeSi(Li)

moveablemirror

shielding

object

xy table

laser beam

foil

Depth profiling of the “14 Nothelfer” by Lucas Cranach the Elder

PIXE analysisat two differentproton energiesprobes material at different depth

The red robe of the holy Christopherus

Depth distribution of Hg and Pbindicates that the deeper layerof the coat was painted withminium Pb3O4 and the surfacelayer with vermilion HgS.The spectrum shows the

three L-transitions for Hg &Pb at two different energies.

1.52.12.5

33.7

4Hg

Pb

0

10

20

30

40

50

60

70

content [%]

energy [keV]element

Hg

Pb

HgS depth profileHgS

Pb3O4

IHg Calculate the range of the 2 MeV and the 4 MeV proton beam in HgS; assume pure Hg! (A=200, ρ=13.6 g/cm3). The thickness of the HgSlayer corresponds to the 50% Hg X-ray intensity.Rair(2 MeV)=8 cm, Rair(4 MeV)=22 cm

R

R

HgS thickness corresponds to about

Hg

Hg

( ) ..

[ ] .

( ) ..

[ ] .

2 32 10200

1368 2 7 10 27

4 32 10200

13622 7 3 10 73

50

4 3

4 3

MeV cm cm m

MeV cm cm m

m

≈ ⋅ ⋅ ⋅ = ⋅ =

≈ ⋅ ⋅ ⋅ = ⋅ =

− −

− −

µ

µ

µ

Art History Motivation: 19th century painting

Christofano Allori (1615)Pitti Palace, Firenze

• many copies of Allori, even by himself

• this copy:unknown artist19th century??

• high quality of painting:(brushstroke...) ⇒ much older?

trust collection, Berlin

copy of Allori: indirect dating

• analytical task: identification of pigments used (indirect dating by pigment chronology)

• paint layers > 100 µm thick⇒ high proton energies necessary

• 15 different spots analysed on the painting

• on all but one spot: only lead, iron, calcium

19th century or much older?• stylistic evaluation not sufficient• more “solid” arguments: chronology of pigments

• collaboration with restaurateurs/art historians

copy of Allori: yellow colour

• Fe, Pb, Ca• from Fe Kα/Kβ:

iron on top of lead⇒ most probably yellow ochre

• no Cd, Cr ... ⇒ modern pigments can be excluded

copy of Allori: blue colour

• the only spot without Fe ⇒ Prussian Blue excluded (after 1735)

• no Co, Cu ⇒ Smalt, Cobalt Blue, and Azurite excluded

• ⇒ either ultramarine (Na, Al) or indigo (organic)both “invisible” for PIXE (in air), both used since antiquity

PIXE in the analysis of metal surface structure

Because of the large stopping power of high Z material(metals) for charged ion beams, protons cannot penetrate deeply into metal material. Nevertheless PIXE emerged as a very successful method for studying metal surface layers to learn about ancient metal treatment techniques.

e.g. surface analysis ofgilded metal artifactslike this drinking cup.

The thickness of gold gildingGold has the atomic number A=198 and a density of ρ=19.3 g/cm3.

R

A gold gilding layer of up to thickness can be investigated,to penetrate through thicker layers higher beam enery is required(example E = 10 MeV, R = 115 cm):

R

Au

p air

Au

( ) ..

[ ] .

( ) ..

[ ] .

4 32 10198

19 322 51 10 51

50

10 32 10198

19 3115 2 7 10 270

4 3

4 2

MeV cm cm m

m

MeV cm cm m

≈ ⋅ ⋅ ⋅ = ⋅ =

≈ ⋅ ⋅ ⋅ = ⋅ =

− −

− −

µ

µ

µ

A gold gilding of up to 50 µm thickness can be investigated.To penetrate through thicker layers higher beam energy is required!

Penetration through surface layers(lacquer, patina, …)

• range of 4 MeV protons in plastic:

~ 0.25 mm

⇒ use of 68 MeV protons:

energy loss in 1 mm plastic(ρ ≈ 1 g/cm3): ~ 1 MeV

small lateral straggling

0 1 2 3 4 5 6 7 8depth (mm)

plas

ticco

pper

protons

X-rays

The microstructure of surface layersTwo faces of Egyptian egidaca 500 BC, (Louvre, Paris)

Depth profiling of surface with highenergy proton PIXE techniques to obtain, composition, structure andcorrosion properties ⇒ identification of original surface below material and corrosion build-up.

Sacred Amon worshipper Karomama, ca 820 BC - 22nd dynasty, (Louvre, Paris)

Bronze statuette, inlaid with gold, silver, black a white paste (eyes)

Karomama, daughter of the Theban Priest Nimlot of the southern empire. She married Takelat II of the north cementing the union of the southern and northern Egyptian empire.

Among the Egyptian antiquities was a statuette of Queen Karomama, of the twenty-second dynasty. It was thickly covered with green rust. The conservators suspected it was no ordinary example of bronze and it was resolved to carefully remove the coating. As the operation went on the character of the metal changed. Finally it was discovered that the bronze was damascened with gold and silver, and that much ornamentation was spent over the royal robes. (Arthur Lee 1890)(report on original analysis of surface corrosion.)

The surface of Karomama

Surface Deterioration of BronzePIXE scan: 50x150µm2

• 0.37 % chlorine concentration 15µm into corrosion layer

• 0.12 % chlorine concentration >50µm depth

Cu

SnNi

Pb

Corrosion ⇒ Copper chlorid

Metal Soldering

Myrtle wreath, gold, Greek/Macedonian; 4th century BC

Analysis of soldering technique for conservation & reconstruction

Main tube of diadem

Gold leafof diadem Gold-copper

alloy

AuAu

Fe

AuAg

Au

Au

Au

Ag

Au

Au

Cu

Cu

Ag

Au

Zr

Zr

AgZr

Au

The Achemenide Pendant

Excavated from Iranian tombmotif represents deity with twobirds flying in front. 28 old ballssoldered to tubes bent from thinold sheets and soldered together

4th century BC

PIXE view of the Achemenide pendant

Relief work with fairly constant Au and A content; Fe showsat joints and solder points, tube shows high Cu concentration

PIXE analysis of solder joints

gold

silver

copper

A DCB

A DCB

ADCB

Solder connections clearly recognizable; composition of eachsolder alloy reveals ancient soldering technique: • Brazing with Cu-Ag-Cu alloy at point A,B happened at T≈800oC with slow

cooling.• At C joint by local fusion of elements at T≈1000oC, reduction of less noble

elements• at D copper diffusion bonding at T≈900oC, Cu diffuses into Au at T<Au

melting point providing very hard bond.

Cadmium and Forgery

supposedly from the 1st century AD. The three center medallions show images of Vespasian, Titus, Domitian.

The Vespasian necklace,

Assumption is that Cadmium in ancient metalwork indicates

forgery!

Detailed Analysis of medallionSystematic micro-beam analysis

Reveals Cd enrichment at solder points

Micro-beam analysis of Cu-Ag-Au solder

Copper

Cadmium

Silver

Position in mm across solder point0 0.2 0.4 0.6 0.8 1.0

However, Cd can be in ore material. Modern solders show anti-correlation between Cadmium and Copper. This solder shows correlation between Cd and Cu which indicates ancient origin!

Authenticy check for ship wreck coins

Nuestra Senora de Atocha

Treasures from the Atocha

Doubts about the authenticy of some of the “Atocha Escudos” on the market

Analysis of Spanish Escudos18th century escudo18th century escudo fake

Au Ag Fe Cuescudo 1

escudo 2escudo 3

escudo 4suspect coin

0102030405060708090

100

cont

ent [

%]

metal

coin

s

metal content of Spanish Escudo

escudo 1escudo 2escudo 3escudo 4suspect coin

metal content of Spanish Escudo

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

escudo 1 escudo 2 escudo 3 escudo 4 suspect coin

coin

cont

ent

[%] Cu

FeAgAu

Suspect coin hasconsiderably higherAu content and lessAg content thanSpanish Escudo

Nature of ink and pigments with PIXEPIXE has developed into a major analytical tool(like X-ray fluorescence) to investigate ink and pigments in old manuscripts and parchments.

The main goal is to understand ancient productionprocesses and the associated chemical techniques.Further goals are:• to identify authors and artists of ancient paintings • to detect and identify forgeries.

gallic acid + FeSO4.7H2O + water‡ iron-gall ink

Nature of ink and pigments with PIXERitualistic talmudic texts had to be written with special ink. During the 12th and 13th century a bitter dispute between talmudic scholars about thequestion which kind of ink does reallyfulfill the ritualistic requirements:• indian ink used by French Jews• gall ink used by German JewsA decision was made not to accept iron- but only copper vitriol since thelast 6th century entry into the Talmud(summary of ancient Rabbi decisions)mentioned gall-apples & copper vitriol.

PIXE analysis of parchment shows strong iron content, in disobedience of the decision

Trionfo d’Amore Botticelli Drawing

The drawingis attributed to Botticellithe author of the incipit isunknown!

Pigment analysis with PIXE todetermine the technique and origin of paint.

Petrach manuscript, Biblioteca Classense Ravenna, Fiesole

PIXE analysis of Trionfo d’amoreBook holder construction to focus beam onto the seriesof pre-selected points in the drawing.

Paint analysis• The results showed that ochres

with addition of a lead base pigment, were used to obtain the brown colour.

• Iron-gall ink was used to trace the drawing.

• Lead point was used in the preparation of the drawing.

• It was not possible to identify the Lilac pigment used.

• The blue colour of the sky is a lead based pigment deposited on top of an underlying mixture of blue pigments.

Ink and paper of the Gutenberg bible

Analysis of many single letters showed that ink had unusually high copper (Cu), nickel (Ni), and lead (Pb) concentration ⇒ high printing quality!

Deep black ink after 500 years

Letter identification through PIXE

Use of the lateral resolution of a microprobe permits the study of small details in the material. For example PIXE analysis of paper content combined with statistical methods leads to the identification of faint letters.

Greek handwriting ofletter χ on papyrus

photograph

PIXE image

Comparative datingGalileo dated his writings only infrequently, PIXE analysis of inkMay provide clues toward development of thought and ideas. Un-dated manuscript can bePlaced in time and context byPIXE analysis of ink.

Hand-made ink showed differences from batch to batch

Summary PIXE

PIXE is very similar to XRF, the mechanism for exciting the atomsto generate the characteristic X-rays is not based on X-ray irradiationof the sample but on the bombardment with high energy particles –typically protons up to 10 MeV. The disadvantage to XRF is, that onlysmall areas can be studied to small depths. For a global study (~cm2

areas) of the chemical characteristic of a sample XRF is the better method. For the study of mm2 to mm2 areas PIXE is the superior approach. Its large advantage to XRF is that two or three dimensional images of the elemental distribution In the sample can be produced with high spatial resolution. Depth profiling is possible within a fairly limited depth range of 0.1mm only. Like in XRF studies the K-and L-transitions of the low to high Z elements are the main signatures.